System and method for controlling a combustion state in a multi-cylinder engine for a vehicle

Abstract

A system and method for controlling combustion state for an internal combustion engine during engine idling which measures the angular speed of the engine cylinders for a certain interval whenever a predetermined crank angle is reached, and detects a combustion state of a given cylinder in the combustion stroke when the engine is idling according to change in the angular speed. The system (method) also divides the engine cylinders into a plurality of cylinder groups, each group having a pair of engine cylinders, the angular speeds in each pair of engine cylinders (cylinder group) are compared and the ignition timing and/or fuel injection quantity is corrected so that the angular speed of the pair of cylinders (cylinder group) which is higher than that of the other cylinder groups is reduced and, for the pair of cylinders in which the angular speed is slower, corrects the ignition timing and/or fuel injection quantity in the reverse direction to the corrected ignition timing and/or fuel injection quantity by the same quantity so that balance between the angular speeds of the pairs of cylinders is taken, whereby the ignition timing and fuel injection quantity is corrected so that a total sum of the correction quantities for all cylinders in the case of the ignition timing and/or fuel injection quantity always becomes zero.

What is claimed is: 
     
       1. A system for controlling combustion state during idling for a multi-cylinder engine, comprising: (a) first means for detecting engine operating conditions;   (b) second means for detecting an engine idling state;   (c) third means for detecting rotations of an engine crank shaft, the third means outputting a first signal by which a cylinder in a combustion stroke is identified by number, and a second signal corresponding to a predetermined unit crank angle;   (d) fourth means for measuring an angular speed for a certain interval whenever a predetermined crank angle is reached and detecting a combustion state of one of the cylinders in the combustion stroke according to a change in the angular speed when the engine is idling;   (e) fifth means for calculating change quantities of the angular speed for a predetermined interval with respect to the crank angle for each engine cylinder and for calculating correction quantities for the respective cylinders on the basis of the change quantities so that a difference between the change quantities for the respective cylinders become a predetermined value;   (f) sixth means for calculating a basic ignition timing on the basis of the engine operating conditions and for correcting the basic ignition timing for each engine cylinder according to one of the correction quantities for the corresponding cylinder derived by the fifth means when the engine is transferred to an idling condition;   (g) seventh means for igniting air-fuel mixture sucked into the corresponding cylinder at a timing based on the corrected basic ignition timing derived by the sixth means;   (h) eighth means for calculating a basic fuel injection quantity on the basis of the engine operating conditions and correcting the basic fuel injection quantity for each engine cylinder according to the correction quantity for the corresponding cylinder derived by the fifth means when the engine is transferred into an idling condition; and   (i) ninth means for supplying fuel into the corresponding engine cylinder, the quantity of which is determined according to the basic fuel injection quantity corrected by the eighth means.   
     
     
       2. A system as set forth in claim 1, wherein the fourth means measures a time duration Ti between a first crank angular position θ 1  and a second crank angular position θ 2 , calculates a change in the number of revolutions per time, a difference in the angular speed Ne using the following equations:   Ti=θ.sub.2 -θ.sub.1                            (1)       ΔNe=K/Ti-K/T.sub.i-1                                 (2)     wherein K denotes a constant, T i-1  denotes Ti derived one combustion stroke before the present combustion stroke.   
     
     
       3. A system as set forth in claim 2, wherein the fifth means calculates an average value ΔNe for N cycles of the engine revolutions for each cylinder: ΔNe=ΔNe/N; and stores the average value ΔNe into a memory location according to the number of cylinders CYL to accumulate the value of ΔNe. 
     
     
       4. A system as set forth in claim 3, wherein the fifth means counts the number of times n the accumulation is carried out, determines whether the number of times the accumulation of ΔNe is carried out has reached N number of times, and calculates an average value of ΔNe per cycles, ΔNe.sub.(CYL). 
     
     
       5. A system as set forth in claim 4, wherein the number of cycles N averaging ΔNe is a predetermined power of 2. 
     
     
       6. A system as set forth in claim 5, wherein the number of cylinders is four and wherein the fifth means compares the average values of ΔNe in first and second cylinders, determines whether an absolute value, of a difference between the average values ΔNe 1  and ΔNe 2  is greater than a predetermined value Nadv, determines whether ΔNe 1  is greater than ΔNe 2  when |ΔNE1|>Nadv, adds a first correction quantity AdvA of the ignition timing which corrects an unbalanced state of first and second cylinders by ΔAdv, when ΔNe 1  <ΔNej 2 , and subtracts ΔAdv from the first correction quantity, when ΔNe 1  >ΔNe 2 . 
     
     
       7. A system as set forth in claim 6, wherein when |ΔNE1|≦NAdv, the fifth means determines whether an absolute value of a difference between the average values in the third and fourth cylinders is greater than the predetermined value Nadv, determines whether ΔNe 3  is greater than ΔNe 4  when |ΔNE2|>Nadv, adds a second correction quantity AdvB of the ignition timing which corrects the unbalanced state between the third and fourth cylinders by ΔAdv, when ΔNe 3  <ΔNe 4 , and subtracts Adv from the second correction quantity, when ΔNe 3  >ΔNe 4 . 
     
     
       8. A system as set forth in claim 7, wherein when |ΔNE2|≦Nadv, the fifth means determines whether an absolute value |ΔNCYL| of a difference between an average value ΔNCYL1 of ΔNe in a first group having the first and second cylinders and an average value ΔNCYL2 of ΔNe in a second group having the third and fourth cylinders is greater than the predetermined value Nadv, determines whether ΔNCYL1 is greater than ΔNCYL2 when |ΔNCYL|>Nadv, and adds a third correction quantity AdvE of the ignition timing which corrects an unbalanced state in the corresponding cylinder group by ΔAdv when ΔNCYL1<ΔNCYL2, AdvE←AdvE+ΔAdv, subtracts ΔAdv from the third correction quantity AdvE when ΔNCYL1>ΔNCYL2, AdvE←AdvE+ΔAdv. 
     
     
       9. A system as set forth in claim 8, wherein when |ΔNCYL|<Nadv, the sixth means derives fourth correction quantities for the respective cylinders in such way that in the fourth quantity for the first cylinder, the first correction quantity is added, DAdv1 ←AdvA+AdvE, in the fourth correction quantity for the second cylinder, the first correction quantity is subtracted, DAdv2←(-AdvA)+AdvE, in the fourth correction quantity for the third cylinder, the second correction quantity is added, DAdv4←AdvB-AdvE, and in the fourth correction quantity for the fourth cylinder, the second correction quantity is subtracted, DAdv4←(-AdvB)-AdvE. 
     
     
       10. A system as set forth in claim 9, wherein the fifth means compares the average values of ΔNe in first and second cylinders, determines whether an absolute value, of a difference between the average values ΔNe 1  and ΔNe 2  is greater than a predetermined value Nadv, determines whether ΔNe 1  is greater than ΔNe 2  when |ΔNE1|>Nadv, adds a fifth correction quantity FueA of fuel injection quantity which corrects an unbalanced state of first and second cylinders by Fue, FueA←FueA +ΔFue, when ΔNe 1  <ΔNe 2 , and subtracts ΔFue from the fifth correction quantity, FueA←FueA-ΔFue, when Ne 1  >Ne 2 . 
     
     
       11. A system as set forth in claim 10, wherein when |ΔNE1|≦NAdv, the fifth means determines whether an absolute value of a difference between the average values in the third and fourth cylinders is greater than the predetermined value Nadv, |ΔNe 3  -ΔNe 4  |=|ΔNE2|, determines whether ΔNe 3  is greater than ΔNe 4  when ⊕ΔNE2|>Nadv, adds a sixth correction quantity FueB of the fuel injection quantity which corrects the unbalanced state between the third and fourth cylinders by ΔFue, FueB←FueB+ΔFue, when ΔNe 3  <ΔNe 4 , and subtracts ΔFue from the sixth correction quantity, FueB ←FueB-ΔFue, when ΔNe 3  >ΔNe 4 . 
     
     
       12. A system as set forth in claim 11, wherein when |NE2|≦Nadv, the fifth means determines whether an absolute value |ΔNCYL| of a difference between an average value ΔNCYL1 of ΔNe in the first group having the first and second cylinders and an average value ΔNCYL2 of ΔNe in the second group having the third and fourth cylinders is greater than the predetermined value Nadv, determines whether ΔNCYL1 is greater than ΔNCYL2 when |ΔNCYL|>Nadv, and adds a seventh correction quantity FueE of the ignition timing which corrects an unbalanced state in the corresponding cylinder group by Fue when ΔNCYL1<ΔNCYL2, FueE←FueE+ΔFue, subtracts ΔFue from the third correction quantity FueE when ΔNCYL1>ΔNCYL2 FueE←FueE+ΔFue. 
     
     
       13. A system as set forth in claim 12, wherein when |ΔNCYL|<Nadv, the sixth means derives eighth correction quantities for the respective cylinders in such way that in the eighth quantity for the first cylinder, the sixth correction quantity is added, DFuel ←FueA+FueE, in the eighth correction quantity for the second cylinder, the sixth correction quantity is subtracted, DFue2←(-FueA)+FueE, in the eighth correction quantity for the third cylinder, the seventh correction quantity is added, DFue4←FueB-FueE, and in the eighth correction quantity for the fourth cylinder, the seventh correction quantity is subtracted, DFue4←(-FueB)-FueE. 
     
     
       14. A system as set forth in claim 5, wherein the number of engine cylinders is six. 
     
     
       15. A system as set forth in claim 5, wherein the number of engine cylinders is eight. 
     
     
       16. A system for controlling a combustion state for an internal combustion engine during engine idling, comprising: (a) first means for detecting engine operating conditions;   (b) second means for detecting an engine idling state;   (c) third means for detecting rotations of an engine crankshaft, the third means outputting a first signal by which a cylinder in a combustion stroke is identified by a number and a second signal corresponding to a predetermined unit crank angle;   (d) fourth means for measuring an angular speed for a certain interval whenever a predetermined crank angle is reached and detecting a combustion state of one of the cylinders in the combustion stroke according to a change in the angular speed when the engine is idling;   (e) fifth means for dividing the engine cylinders into a plurality of cylinder groups, each group having a pair of the engine cylinders, for comparing angular speeds in each pair of the engine cylinders, for correcting at least one of ignition timing and fuel injection quantity so that the angular speed of a pair of cylinders which is higher than that of at least one other cylinder group is reduced and, for a pair of cylinders in which the angular speed is slower, correcting at least one of ignition timing and fuel injection quantity in the reverse direction to the corrected at least one of ignition timing and fuel injection quantity by the same quantity so that a balance between the angular speeds in the pairs of the cylinders is taken;   (f) sixth means for comparing the angular speeds in the cylinder groups, for correcting at least one of the ignition timing and fuel injection quantity so that the angular speed of the one cylinder group in which the angular speed is higher than that in at least one other cylinder group is reduced and, for the group of the cylinders in which the angular speed is slower, correcting at least one of the ignition timing and fuel injection quantity in the reverse direction to the corrected at least one of ignition timing and fuel injection quantity by the same quantity, so that a balance in the angular speed between the cylinder groups is taken, the fifth and sixth means correcting the ignition timing and fuel injection quantity so that a total sum of the correction quantities for all cylinders in the case of the at least one of ignition timing and fuel injection quantity always becomes zero.   
     
     
       17. A method for controlling a combustion state for an internal combustion engine during engine idling, comprising the steps of: (a) detecting engine operating conditions;   (b) detecting an engine idling state;   (c) detecting rotations of an engine crankshaft, the third means outputting a first signal by which a cylinder number in a combustion stroke is identified and a second signal corresponding to a predetermined unit crank angle;   (d) measuring an angular speed for a certain interval whenever a predetermined crank angle is reached and detecting a combustion state of one of the cylinders in the combustion stroke according to a change in the angular speed when the engine is idling;   (e) dividing the engine cylinders into a plurality of cylinder groups, each group having a pair of the engine cylinders, for comparing angular speeds in each pair of the engine cylinders, for correcting at least one of ignition timing and fuel injection quantity so that the angular speed of a pair of cylinders which is higher than that of at least on other cylinder group is reduced and, for a pair of cylinders in which the angular speed is slower, correcting the at least one of ignition timing and fuel injection quantity in the reverse direction to the corrected at least one of ignition timing and fuel injection quantity by the same quantity so that a balance between the angular speeds in the pairs of the cylinders is taken;   (f) comparing the angular speeds of all cylinder groups, for correcting the at least one of ignition timing and fuel injection quantity so that the angular speed of a cylinder group in which the angular speed is higher than that of another cylinder group is reduced and, for a cylinder group in which the angular speed is slower, correcting the at least one of ignition timing and fuel injection quantity in the reverse direction by the same quantity, so that a balance in the angular speed among all cylinder groups is achieved, the steps (e) and (f) correcting the ignition timing and fuel injection quantity so that the total sum of the correction quantities for all cylinders always becomes zero.